In recent years, strongly acidic electrolyzed water generated at an anode side upon electrolysis of a diluted solution of sodium chloride and the like has attracted attention in various fields because it shows a powerful bactericidal effect. Factors that strongly acidic electrolyzed water shows a bactericidal capacity include the followings: characteristic values, a low pH of pH 2.7 or less and a high ORP of +1100 mV or more, for strongly acidic electrolyzed water are outside the viable ranges, ORP +900 to −400 mV and pH 3 to 10 for microorganism (for example, see Nonpatent Literature 1). However, according to subsequent studies, currently popular theory is that it is due to the oxidizing power of effective chlorine which primarily comprises hypochlorous acid generated upon electrolysis (for example, see Nonpatent Literatures 2 or 3).
Radical species generated at an electrode are thought not to be involved in the bactericidal activity of strongly acidic electrolyzed water (for example, see Nonpatent Literature 4). That is, in general, a radical is highly reactive, unstable and short-lived since it has an unpaired electron. A hydroxyl radical is highly reactive and short-lived among others, and often attributed to be an agent of the activity of acidic electrolytic water. However, it is thought that a hydroxyl radical cannot be a basis for the bactericidal activity of acidic electrolyzed water because a signal from a hydroxyl radical was not detected in the analysis using the electron spin resonance (ESR) spin trap method (for example, see Nonpatent Literatures 5 or 6), and a high bactericidal activity is maintained in acidic electrolyzed water stored for a long time after generation (for example, see Nonpatent Literature 7).